Extraction of spatial aerosol distributions from multispectral light extinction measurements with computed tomography

We combine optical remote sensing with computed tomography to determine simultaneously (a) the concentration and (b) the size distribution of particles at every pixel in a plane that slices through an aerosol. Light-extinction measurements are made along intersecting paths that pass through the plane. The spatial distribution of extinction coefficients at multiple wavelengths is obtained by an edgebraic image-reconstruction technique (ART3). The size distribution of the aerosol at every pixel in the plane is obtained by inversion of the Fredholm integral equation. Computer simulations of this procedure were conducted. Extinction coefficients were found at all pixels in the plane at multiple wavelengths. Aerosol size distributions were retrieved at four pixels. Results of this analysis show that four projection angles were sufficient for reconstruction of extinction coefficient distributions in the plane. The technique can tolerate up to 10% random, normally distributed noise in the measurements. The size distributions at the four pixels were close to the true distributions. The size of the smallest feature that needs to be recovered should be larger than the ray spacing. We were able to delete three of every four rays and still get good reconstructions.